1. Field of the Invention
This invention relates to a process of and an arrangement for inking and doctoring a printing plate for use in a pad printing machine. In particular, the invention concerns a process and an arrangement where ink is applied to a design provided on a printing plate, the plate is doctored by a suitable doctor blade and then ink is picked up from recessed parts of the printing plate by means of a pad provided as a part of the printing machine.
2. Discussion of the Prior Art
In known pad printing machines, a printing plate having a design or pattern etched therein usually is mounted within an ink tray, a doctor blade being arranged to scrape excess ink off the surface of the plate and so to leave ink in the recessed parts of the plate.
The prior arrangements generally have been of one of two types. In one, the ink tray is fixed while the doctor blade and so on are arranged to be movable horizontally over the surface of the plate. In the other, the doctor blade and so on are fixed, and the ink tray is moved horizontally below the blade. These arrangements both require the ink tray to be open from the top, so that thinners or other components of the ink evaporate over a period of time. Consequently, if printing is to be continued for some time, the ink must appropriately be replenished, for example, by means of an automatic thinner adding device. Also foreign matter may easily fall into the ink tray and so contaminate the ink.
In an attempt to overcome the difficulties of an open ink try, there has been a proposal to contain the ink within a pot which bears on the printing plate and has an opening in that region to permit the application of ink to the plate. This arrangement however requires a very high degree of flatness for the printing plate and so is applicable mainly to printing plate having a relatively small printing area.
A further problem with the known arrangement is that the two steps, of doctoring the printing plate and of reapplying the ink, are both necessary in each cycle of the printing operation and so it has been difficult to accomplish continuous printing operation at a relatively high speed.